The synthetic opioids are often sold over the internet by labs in China.

Already this year, the DEA has characterized five synthetic opioids as “Schedule I,” which means they have no medical purpose and can lead to abuse.

The Journal wrote:

Furanyl fentanyl, a relative newcomer, didn’t appear in a national database that tracks drug seizures until December 2015, according to the DEA. It has quickly emerged as a serious killer among designer opioids. NMS Labs, a major private lab that works with states around the U.S., has tallied 325 deaths linked to furanyl fentanyl this year through October.

The legal form of fentanyl is a strong, up to 50 times the potency of heroin, pain reliever that often is used to help cancer patients manage serious pain. But bootleg versions of fentanyl, often made in China and then mixed into the heroin supply or included in counterfeit prescription pills have amplified the U.S. opioid crisis.